So, here is a little helpful information that y'all may or may not have known. This information was very costly...at least to me. I am fortunate enough to own one 2004 Columbia Edition 4.7 H.O. with 160,000 miles on it. Back in September, the valve seat on cyl number 2 intake valve launched a guerilla warfare style attack on that same cylinder. No survivors. Piston, rod, cylinder head and block wall. Jacked. Pulled engine. Re-ringed all 8. Reworked heads on both sides. New piston on #2. Oil pump. Rear main. Sensors. Reassembled. Ran great for 12 minutes. Then a grenade went off. Knocked louder than a Cash for Clunkers poison victim. Cracked it back open. Same catastrophic damage. Seems ( i know now....) a good deal of the pulverized valve seat material lodged itself in the plastic manifold- where it cannot be seen. It lay there, waiting to undo hours of diligent repairs. Lesson= if your engine { 3.7 or 4.7 or 5.7} suffers catastrophic damage to any cylinders you MUST painstakingly clean the upper manifold out or replace it. Engine runs wonderful now and I hope to run this Jeep until I tire of modding it.